That makes sense. If it wasn't *closing* properly, then it would allow boost to blow through the crankcase and out the breather. This would also essentially behave like a boost leak, causing boost to take longer and require higher rpms to build up. Sounds like that was the root problem.Originally Posted by Bkeef
No. The spring holds the check valve closed, and a closed check valve is what is necessary to avoid a boost leak into the crankcase. Weakening the spring would make it open more easily, which may allow the PCV system to operate more efficiently at part throttle cruising, but would have no effect on performance at higher engine loads... unless it is weakened so much that it doesn't reliably close, and that would bring you back to the same problem you just solved.
One attribute of check valves is "cracking pressure"... the amount of pressure required to "crack" the valve open. The best option for this application would be a zero cracking pressure valve. It would basically behave as if it didn't exist at all any time there was no boost, and the PCV system would work exactly as originally designed. As soon as manifold pressure crossed into the positive boost range, the valve would close and prevent boost from entering the crank case.
The check valve in the turbo kit seems to require quite a bit of pressure to crack it open. That means that at certain engine loads when the stock PCV valve would normally allow manifold vacuum to suck some air from the crankcase, the check valve is actually staying closed and preventing airflow through the crankcase. I'm thinking of replacing it with a valve that has a low cracking pressure (0.3 psi). That's the lowest cracking pressure I was able to find for a check valve that is the right size, etc. Dan at Prodigy was not able to obtain the specs for the check valve they use, so I'm not even certain that my replacement would be an improvement.
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